An ordinary grooved slot rod 11 is shown in FIG. 2. Slot rod 11 includes a body 13 having a single or plurality of spiral grooves 14 formed on the outer circumferential surface thereof and extending at a certain spiral pitch along the longitudinal direction of the body. A tension-withstanding wire 12 is provided in the central portion of the body. To assemble a ribbon-slot type optical fiber cable including rod 11 and optical fiber tapes, the rod is payed out from a reel, and the ribbons are inserted into the spiral grooves 14 of the body 13 of the rod by an insertion device. Since the spiral grooves 14 are formed spirally along the longitudinal direction of the body 13, the optical fiber ribbons need to be guided into the grooves.
FIG. 3 shows a conventional apparatus for paying out a slot rod 11. The apparatus includes a reel 101 having a rod 11 wound thereon in advance, a frame 102, a rotary shaft 103 supporting the reel at one end of the frame so as to pay out the rod in a direction perpendicular to the axis of the shaft, a disk 104 fastened to the frame, a pair of rollers 105 supporting the disk, a support member 106 for supporting the frame, and guide rollers 107 and 108 attached to the frame to guide the rod. The frame 102 can be rotated about the paying-out direction of rod 111, synchronously with the turning of the spiral grooves 14 thereof, by a driver (not shown). A caterpillar-type braking device 109 is provided next to the apparatus in order to apply a desired tensile force to the rod 11. The braking device includes caterpillars 112 supported by pairs of rollers 110 and 111 extending over and under the rod 11 being payed out. The caterpillars 112 can be rotated about the paying-out direction of the rod 11, synchronously with the turning of the spiral grooves 14 thereof, as well as the frame 102 of the apparatus. In the conventional apparatus, the reel 101 is rotated about the rotary shaft 103 and the frame 102 is rotated about the paying-out direction of the rod 11, so that the rod is unwound from the reel and thus, payed out. In the braking device, the rod 11 is pushed between the upper and the lower caterpillars 112 so that the desired tensile force may be applied to the rod.
The tensile force applied to rod 11 by the caterpillar-type braking device 109 while being payed out by the conventional apparatus, is unstable due to changes in the pushing forces of the caterpillars 112 on the rod, and to frictional forces on the rotary sliding portions of the apparatus. Thus, the conventional apparatus does not ensure a consistent tensile force in operation. In addition, since the braking device 109 is provided separately from the paying-out apparatus, the size of an entire machine is large.